Generally, an electric car is a vehicle which is driven using electric power. Electric cars appeared in the end of the 1880s, and have been used as transport means like cars, trucks and buses etc. The electric cars are known to efficiently use kinetic energy of a vehicle through an electric car control device, in which a power storage unit is combined with an inverter configured to drive an electric motor of the electric car, mounted in the vehicle, and storage of surplus regenerative power generated upon braking of the vehicle in the power storage unit, which is then used upon acceleration of the vehicle or a decrease in line voltage. In particular, a battery management system (BMS), which functions to improve gas mileage and ensure safety by optimizing the control of batteries in the electric car, has been applied to and used in such electric cars. Also, BMS is realized on a PCB provided with a transformer module for use.
Referring to FIG. 1, such a conventional transformer PCB device for an electric car is configured to include a plurality of battery cells 70a-n configured to supply power to an electric car (not shown); transformer PCBs 71a-n mounted to be connected to the plurality of battery cells 70a-n in a serial or parallel electrocircuit mode; and a charging unit 72 mounted at the transformer PCBs 71a-n to rectify a supply voltage applied from the outside and apply the rectified supply voltage to the battery cells 70a-n. 
In this case, a plastic is generally used as a material in the transformer PCBs 71a-n, and wires required for serial or parallel connection of the battery cells 70a-n are installed in the transformer PCBs 71a-n. Also, the respective electrocircuit connection between the transformer PCBs 71a-n and the battery cells 70a-n is performed by patterning copper tabs 73a-n on the transformers PCB 71a-n, as shown in FIG. 2. For example, the copper tabs 73a-n formed on such conventional transformer PCBs 71a-n are formed so that the Cu thickness is maintained with a thickness of 2 oz (70 μm) to 4 oz (140 μm) on both surfaces of a base substrate 74 of each of the transformer PCBs 71a-n. 
Meanwhile, such a conventional transformer PCB device for an electric car is operated as follows. First, when a supply voltage is applied to the charging unit 72, the charging unit 72 functions to convert the applied supply voltage, for example, an alternating current voltage, into a given charging voltage, rectify the charging voltage, and charge the charging voltage in each of the battery cells 70a-n through electric circuits formed on the transformer PCBs 71a-n as copper tabs 73a-n. Then, the above-described charging voltage is applied to each of the battery cells 70a-n via the copper tabs 73a-n of the transformers PCB 71a-n, that is, the copper tabs 73a-n having a thickness of 2 oz (70 μm) or 4 oz (140 μm). In this case, an electric current of the supply voltage has a current behavior, and thus is supplied to each of the battery cells 70a-n by the copper tabs 73a-n of the transformer PCBs 71a-n, that is, the copper tabs 73a-n having a thickness of 2 oz (70 μm) or 4 oz (140 μm), followed by a conventional charging process.
However, such a conventional transformer PCB device for an electric car has a transformer PCB structure in which the copper tabs having a thickness of 2 oz (70 μm) or 4 oz (140 μm) are formed on both surfaces of a transformer PCB. Therefore, when battery cells are safely and effectively charged with a supply voltage, the plurality of transformer PCBs should be connected to each other for use. As a result, an increase in part insertion space, and thus an increase in weight may have a negative influence on the fuel efficiency of a vehicle. Further, when the copper tabs have different thicknesses, the high error rate or low production yield may be caused during a production process.